In recent years, accompanying with rapid progress of social information, technologies regarding information-related appliances are also rapidly progressing and spreading. Various electronic equipments, communication devices and display device such as CRT, liquid crystal, EL, PDP and FED have been used for televisions, personal computers, displays for showing information at a station or an airport, and for providing other various kinds of information.
It has been worried about an effect of electromagnetic wave irradiated from these electronic equipments or communication devices. For example, the problem that this electromagnetic wave causes malfunction of neighboring machines or bad influence to human body are considered, so that demands for an electromagnetic wave shielding material becomes higher and higher. To comply with such demands, various transparent conductive films (electromagnetic wave shielding material) have been developed. For example, they are disclosed in Japanese Unexamined Patent Publications No. Hei. 9-53030, No. Hei. 11-126024, No. 2000-294980, No. 2000-357414, No. 2000-329934, No. 2001-38843, No. 2001-47549, No. 2001-51610, No. 2001-57110, No. 2001-60416, and the like.
As a process for preparing these electromagnetic wave shielding materials, it has generally been employed a method in which a conductive metal such as silver, copper, nickel, indium, etc., or a conductive metal compound of these metals is formed on a transparent resin film substrate as a metal thin film by a sputtering method, an ion plating method, an ion beam assist method, a vacuum deposition method, or a wet coating method. However, when a film thickness or pattern fine line width is set with a degree that the transparency can be maintained, a surface resistance of the conductive layer becomes so large to cause as to cause small shielding effect, so that there is a problem that, for example, it is difficult to obtain a shielding effect of 30 dB or higher over higher frequency bands of 300 MHz or higher. Accordingly, an electromagnetic wave shielding material having high transparency and excellent in shielding property over higher frequency band region has been desired. Also, in recent years, demands of the electromagnetic wave shielding material are expanded, and a preparation process that is low cost and has high productivity has been desired.
In Japanese Patent Publication No. Sho. 42-23745, a technique for forming a conductive layer comprising physically developed silver according to a silver complex diffusion transfer development method (DTR development method) by applying a silver halide emulsion layer and a silver halide solvent (silver complex salt-forming materials). However, as mentioned above, to comply with a light transmittance with a total luminous transmittance of 50% or more and a conductivity with a surface resistance of 10 ohm/□ (10 Ω/square) or less are simultaneously satisfied, which are required for an electromagnetic wave shielding material in recent years, it could not be accomplished by the technologies disclosed in the above-mentioned patent publications.
Accordingly, an object of the present invention is to provide an electromagnetic wave shielding material having high conductivity and a high total luminous transmittance even when a fine line pattern with a fine line width which causes a higher aperture rate is provided. Another object of the present invention is to provide a process for preparing an electromagnetic wave shielding material having high conductivity and a high total luminous transmittance with low cost and high productivity.
The above-mentioned objects of the present invention have been basically accomplished by an electromagnetic wave shielding material in which a metal is plated by using physically developed metal silver as a catalytic nucleus.
A basic process for preparing an electromagnetic wave shielding material of the present invention comprises dissolving silver halide with a soluble silver complex salt-forming agent to make a soluble silver complex salt, and simultaneously reducing it with a reducing agent (developing agent) such as hydroquinone, etc., to precipitate physical metal silver with an optional fine line pattern on a physical development nuclei, and subjecting to plating with a metal such as copper, nickel, etc., using the physically developed silver as a catalytic nucleus, which applies a DTR development method known as the photographic development method.